Human leukocyte antigen (HLA) genes are located on the short arm of chromosome 6. HLAs are classified into class I molecules (HLA-A type, B type and C type) and class II molecules (HLA-DP type, DQ type and DR type). In specific immune response, when cytotoxic T cells (CTL) recognize cell surface antigens such as tumor cells, transplanted cells and virus infected cells, it is essential to recognize the cells with class I molecules. Class I molecules are present on the membrane surface of almost all cells.
When cells are infected with a virus such as dengue virus, innate immunity is triggered to induce a reaction to eliminate the virus. After that comes specific immune response to induce a reaction to eliminate the viruses.
In specific immune response, the viruses in body fluids are eliminated by neutralizing antibodies. The viruses inside the cell are eliminated by cytotoxic T cells (CTL). Thus, CTLs specifically recognize the viral antigen (CTL epitope) composed of 8 to 11 amino acids presented by the HLA class I molecules on the infected cell surface, and eliminate the viruses by inducing damage to the infected cells. Therefore, it is important to identify such virus-specific CTL epitopes in order to produce preventive and therapeutic vaccines for the viruses.
One of such techniques is described in Patent Document 1, which discloses that an oligopeptide consisting of a certain amino acid sequence is capable of binging to HLA.    Patent Document 1: Japanese Patent Laid-Open No. 8-151396